A beam is a shape that an electromagnetic wave transmitted by using an antenna forms on a surface of the earth. A beam width is determined by an antenna gain. A larger antenna gain indicates a smaller beam width, that is, a narrower beam.
In a propagation process, a signal sent by using an antenna of a base station is easily absorbed and scattered by an obstruction such as rain, fog, or a building. Consequently, a path loss is relatively large. To compensate for the path loss in the propagation process, the base station may send a signal by using multiple antennas and a massive MIMO (multiple input multiple output) technology, so as to generate an extremely large antenna gain.
A beam formed when the base station generates an extremely large antenna gain is extremely narrow, causing a small coverage area of a single beam. To increase a signal coverage area, the base station needs to send a signal by using multiple beams. Even a synchronization signal, a broadcast signal, a control signal, or the like needs to be sent by using a beam. Therefore, user equipment needs to determine a beam in which the user equipment is currently located, so as to better communicate with the base station. However, for any user equipment within the signal coverage area, even though the user equipment detects the signal sent by the base station, the user equipment cannot determine which beam the user equipment is currently located in. Consequently, the user equipment cannot notify the base station of the beam in which the user equipment is located, and the base station cannot further communicate with the user equipment. Therefore, how to determine, according to the signal sent by the base station, the beam in which the user equipment is currently located becomes a problem to be resolved.